The invention related generally to the field of electronic photography, and in particular to a single sensor camera of the type that requires color filter array interpolation.
A typical digital camera uses a single color image sensor to capture a representation of a scene, including a representation of the color in the scene. The colors are separated by a color filter array (CFA) that overlies the sensor and associates each image pixel with a particular color according to the particular color pattern of the CFA. For example, the Bayer CFA (described in U.S. Pat. No. 3,971,065) provides an RGB pattern with a checkerboard arrangement of green pixel sites. Therefore, the primary CFA image signal for each pixel relates to but one color, that is, to either red, green or blue (for a Bayer CFA). After the CFA image is captured, the remaining (missing) colors for each pixel site are interpolated for each pixel from, e.g., surrounding pixels, so that a full resolution interpolated record is generated for each image. Each pixel in the interpolated record therefore has a set of RGB values.
Digital cameras, such as the Kodak DCS 420c camera, store the uncompressed digital images data from a single-sensor color camera (approximately 1024xc3x971536 pixels) on a removable digital hard drive memory. When the camera or memory is connected to a host computer, the images can be imported into an image processing program such as Adobe Photoshop(trademark). A typical flow diagram for such a capture sequence and processing program is shown in FIG. 1, and a representation of the image size for selected stages in the flow diagram is shown in FIG. 2. A CFA image 10 is captured in a capture step 12 by the camera. The CFA images are subsequently processed in a CFA interpolation step 14 as they are imported, using known CFA interpolation, color correction, and sharpening techniques, in order to create a xe2x80x9cfinishedxe2x80x9d RGB image file having a standard size. The finished RGB image file thus contains the CFA interpolated image 16, which has the same number of total pixels as the original image (for example, approximately 1024 xc3x971536 pixels for the DCS 420c camera). Unlike the original image, however, the CFA interpolated image 16 has complete RGB data for each pixel.
To create the final printed images, the imported image is typically adjusted by the user via an image processing stage, such as provided by a program like Adobe Photoshopxc3xa4, to create a final output image 20 of the desired size, which may include only a xe2x80x9ccroppedxe2x80x9d portion 22 of the image captured by the camera. User crop selection is thus performed at a user input stage 23 after CFA interpolation of the image data. More specifically, to provide the appropriately sized output image, the image processing program first crops the 1024xc3x971536 RGB CFA interpolated image data in a cropping step 18, and then uses another interpolation algorithm in an interpolating step 24 to convert from the cropped version of the xe2x80x9cfinishedxe2x80x9d RGB image file to the final desired output image 20. Note that this prior art approach uses two interpolation steps, one (step 14) to interpolate xe2x80x9cmissingxe2x80x9d RGB data from the image sensor while maintaining the 1024 xc3x971536 pixel data array that provides the desired output size. For example, to produce an approximately 7xe2x80x3xc3x9710xe2x80x3 print using a printer with 300 pixels per inch, 2xc3x97 (two times) up-interpolation is used to create a 2048xc3x973072 pixel data array. In addition, this known approach often uses two separate sharpening operations, one on the 1024xc3x971536 pixel CFA interpolated image data following the CFA interpolation step 14, and a second one on the interpolated 2048xc3x973072 pixel image data array just prior to printing.
The prior art approach thus has a number of problems. First, the processing time is longer, since pixels that will be cropped out of the final image are still processed by the CFA interpolation processing. Second, the two interpolation steps provide more interpolation artifacts than would be produced using a single interpolation step. Finally, using two separate sharpening steps can also produce artifacts. What is needed is a digital camera system that enables both interpolation processes to be completed in a single step, to provide both faster processing and improved image quality.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, an electronic still imaging system employs an image sensor comprised of discrete light sensitive picture elements overlaid with a color filter array (CFA) pattern to produce color image data corressponding to the CFA pattern, an A/D converter for producing digital CFA image data from the color image data, and a memory for storing the digital CFA image data from a fixed number of picture elements corresponding to a fixed image size. A user selects at least one output image size different from the fixed image size, such that the output image will have a different number of picture elements than the fixed number of picture elements in the fixed size image. A processor then interpolates full color data for each picture element and produces an interpolated output image having the selected output image size.
According to this invention, the xe2x80x9coriginalxe2x80x9d image data (which is optionally compressed using a numerically lossless or visually lossless technique) is stored in a digital image file on a digital memory and transferred to the host computer. This image file is retained until a final rendered image is created. A xe2x80x9csoft copyxe2x80x9d quality version of the image can be displayed to the user, who can decide to crop the image and to create an output image of any size to be printed, incorporated into other documents, etc. The advantage of the invention is this: To create the final high quality image, the cropped portion of the original pixel data is directly interpolated (and optionally sharpened) in a single stage to create the proper output image size. By directly mapping the input pixels to the desired output pixels in a single stage that includes CFA interpolation, interpolation artifacts are minimized. In addition, if the image is sharpened in this stage, the sharpness of the output image is improved without degradation from artifacts due to multiple sharpening stages.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.